The invention relates to a corrosion-resistant structural shape, which is clad by rolling and welding, and which comprises a base material and a cladding material. In particular the invention relates to clad plates, as well as a method of producing such a structural shape.
For producing corrosion-resistant structural shapes, in particular plates, a method of cladding is used; wherein a base material that may consist of a carbon steel or of an alloyed steel is connected with a corrosion-resistant cladding material. Suitably the connection procedure is effected by rolling a cladding pile consisting of the base material and of the cladding material. Corrosion-resistant alloys are known in various compositions. They have a high content of nickel, molybdenum, chromium, and the like, and are rather expensive materials. In alloys of this kind, however, a precipitation of undesired phase occurs, when the content of alloy elements tending to precipitations amounts to the following percentages: carbon 0.001 to 0.2% by weight; molybdenum 2.5 to 17% by weight; chromium 12 to 25% by weight; nickel 9 to 70% by weight, and silicon 0.01 to 4% by weight. In the art these precipitations are called sigma-phase, chi-phase and lave-phase. A particularly critical limit is considered to exist at a content of nickel and chromium together amounting to 30%.
So as to avoid precipitations in the above mentioned, corrosion-resistant alloys, it is necessary to subject these alloys to a solution heat treatment. The solution heat treatment is normally carried out in a temperature range between from 1175.degree. to 1230.degree.C during several hours. Subsequently the material that has been subjected to a solution heat treatment is quenched in water. When such a solution heat treatment is necessary in the case of a clad structural shape, the entire structural shape, for instance the rolled cladding pile, has to be subjected to the heat treatment. From this it follows that only a base material that can withstand this heat treatment can be used. An unalloyed carbon steel cannot be used because it would be overheated by the high temperatures occurring in the solution heat treatment and hence its mechanical properties would be impaired considerably. As is known, overheating leads to an increase in the grain size, which causes detrimental effects. This is why hitherto in producing corrosion-resistant structural shapes clad by rolling and welding in which the cladding material consisted of a corrosion-resistant alloy of the above mentioned composition, it was necessary to use as base materials only those capable of withstanding the extreme conditions of solution heat treatment. Such materials are austenitic chromium-nickel steels which are, however, very expensive and whole valuable specific properties cannot be utilized sufficiently in the more or less subordinate use as a base material.